Coastal Living Resourceso f Singapore: Proceedings of a Symposium on the Assessment of Living Resources in the Coastal Areas of Singapore. A STUDY OF THE HYDROBIOLOGICAL CONDITIONS OFSUNGEISERANGOON Nigel K.C. Goh and Beverly P.L. Goh Department of Zoology National University of Singapore Lower Kent Ridge Road Singapore 0511 ABSTRACT The physico-chemical conditions, and pelagic and soft-bottom benthic fauna of six stations established along Sungei Serangoon were investigated. Results revealed low dissolved oxygen levels of the water, as well as a low abundance of living benthic fauna. A total of 68 specimens from eight families were recorded, mainly obtained for a single station at the mouth of the river. Trammel nets set overnight yielded 40 specimens of the catfish, Plotosus anguillaris, the most abundant species obtained in this study, 11 specimens of another catfish, Arius sp. and three Gerres sp. (family Gerreidae). Pollution caused by pig farming, refuse dumping and squatter settlements, together with dredging activities in the river are probable reasons for the poor water quality and the paucity of benthic fauna observed. INTRODUCTION Sungei (= river) Serangoon is located on the north-eastern coast of Singapore and drains into the East Johore Strait. The river mouth opens into the sea directly opposite the offshore island of Pulau Ubin (Fig. 1). In the late 1940's; agriculture in the form of market-gardening and livestock rearing became increasingly important in Singapore and many pig and poultry farms were set up in coastal areas. These farming activities were located near rivers such as Sungei Punggol, Serangoon and Seletar where the rivers served both as a source of water for the farms, as well as dumping grounds for farm wastes (Pang, 1987). During the late 1970's, pig farms located within water catchment areas and urban river systems were resited to Punggol where provisions had been made for the large-scale rearing of pigs . In addition, an intensive programme by the government to clean up the Singapore River and Kallang Basin catchment area in 1977 phased out pig farming activities in these southern rivers altogether , relocating them to Punggol (Chia et al., 1988), which led to an increased pollution load in the rivers draining the Punggol area, namely, Sungei Punggol and Sungei Serangoon. Presently, these pig farming activities in the north are also in the process of being eliminated, owing to the move to pha se out pig farming altogether. 45 N Fig. I. Map of Singapore showing Sungei Serangoon . At present, the coastal area of Se,angoon houses a sludge treatment works. In addition, reclamation works which began in the 1960's to develop the area for refuse disposal and industrial and recreational purposes are still in progre ss (Chia et al., 1988). Very little data comprising soft-bottom benthic commun itie has been published in Singapore. Some of the previous work include the early study of the biota and environmental conditions of Punggol River by Chua (1966), and the more recent study of the hydrobiological condition s of Singapore River and Kallang Basin (Chiang , 1985; Yip et al., 1987; Loo et al., 1987). This study is part of the Asean-Australia Coastal Living Resources Project. It is aimed at identifying and quantifying the soft-bottom benthic and pelagic fauna of Sungei Serangoon , and recording the physico-chemical condition s of the river. The results of this study will be indicative of the impacts of intensive agriculture and increasing industrial activity on a riverine system. MATERIALS AND METHODS The pelagic and soft-bottom macrobenthic fauna, and physico-chemical parameters of Sungei Serangoon were investigated on 23 and 24 May 1988 at 6 stations along the river (Fig. 2). 46 East Johor Strait Punggol Road Fig. 2. Map of Sungei Serangoon showing the 6 sampling stations. An Ekman grab (15cm x 15cm) was used to collect specimens of benthic organisms. Three grab samples were made at each station . Bengal rose in 10% formalin was added to the grab samples before they were sorted. A naturalist's rectangular dredge (with 75cm x 20cm opening, and 50cm long polypropylene net bag with stretched mesh size of 2.5cm) was used to collect samples of benthic macrobiota . A 10 minute dredge tow at one knot was taken at each of the six stations. In addition, one trammel net each (30m x 1.5m , stretched mesh size of 4cm) was laid at two stations (stations 4 and 6) and left for 24 hours to sample pelagic organisms. The physico-chemical parameters of temperature, pH, salinity , dissolved oxygen, and conductivity were measured at intervals of 0.5m of the water column at each station. Visibility was also measured using a Secchi disc. Salinity and temperature were measured in situ with a portable YSI model 33 Salinity-Conductivity-Temperature meter. The conductivity of the water was measured using a portable pHOX 52E Conductivity meter, dissolved oxygen with a YSI Model 57 Oxygen meter and pH with an Orion Research Model SA250 pH meter. Grab samples were sorted using 1mm and 2mm mesh size seives while dredge specimens were sorted with 5mm and 7mm mesh size seives. The specimens were preserved in 10% formalin buffered with Borax and, with the exception of the polychaetes , were transferred to 70% alcohol after 24 hours. A BENTHl progamme (Bainbridge , 1988) was used to process and summarize the data obtained. 47 RESULTS Mean recording s of the physical and chemical parameter s mea sured at each station are shown in Table 1. Water temperature recorded at the six station s did not fluctuate substantiall y, ranging from 29.78 °C to 31.88 °C. Likewi se, pH did not vary much, and ranged between 6.86 and 7.47 . Conductivity reading s showed an average of 3.7 X 104).lS for the whole river and also did not fluctuate significantl y between station s. Mean salinity fluctuated from a minimum of 12.5 °loo at Station 2 to a maximum of 18.0 °/oo at station 1 . There was however, no observable gradient in salinity from station 1 to the mouth of the river, as might be expected in an estaurin e environment where there is a mixing of fresh and sea water. Average dissolved oxygen (D.O.) measured was low ( < 1ppm ) at all. stations except stations 1 and 6, which had mean D.O. readings of 3.94ppm and 1.49ppm respectively. Visibility increased from 0.2m at station 1 to 0.5m at station 6. A substantial amount of pollution was observed along the length of the river, with refuse accumulating in several locations on the bank s of the river. Some dredging activity was also observed at the river mouth. In addition , there was a small settlement of squatters along the banks of the river in the vicinity of station 1. Bum boat s were also moored along the river bank at station 1. The stench of hydrogen sulphide was apparent throughout the length of the river and gas bubbles could be seen rising to the surface of the water. Thi s was especially pronounced in the middle reaches of the river but improved nearer the mouth of the river. Very few living benthic organisms were collected in this study . Although numerous shells of the bivalve, Perna, were dredged up at station s 1 and 4, only a total of 68 live specimens from eight families were found , all obtained from one grab and one dredge at Table 1. Mean readings of physico-chemical parameters recorded at the six statio ns along Sungei Serangoon. PARAMETER STN 1 STN 2 STN 3 STN 4 STN 5 STN 6 Temperature (CC) 31 .88 30.50 31.00 30.17 30.17 29.78 pH 7 .13 6.98 7.06 7.51 6.86 7.47 Salinity (0/oo) 18.00 12.50 14. 93 16.50 12.92 13.00 Dissolved Oxygen 3.94 0.23 0.10 0.37 0.16 1.49 (ppm) Conductivity 3.67 3.34 3.78 2.97 3.74 4.74 (X 10000 µS) Visibility (ml 0.20 1.25 0.30 0.30 0.40 o.so 48 station 6, at the river-mouth, and the trammel nets set at stations 4 and 6. The other stations (1, 2, 3 and 5) produced no living benthic fauna, the grabs and dredges drawn up yielding only highly anaerobic mud. A summary of the percentages of all families recorded in this survey is shown in Fig. 3. From the dredge at station 6, 10 gastropods were identified. These were, seven specimens of Nassarius sp. (family Nassariidae), two specimens of Natica sp. (family Naticidae) and one specimen of Solenosteira sp. (family Buccinidae). The grab sample at station 6 produced four annelids of which three specimens were Paraonides sp. (family Paraonidae), and one lospilus sp. from the family Iospilidae . The two trammel nets laid at stations 4 and 6 yielded three families of fish, namely, Ariidae , Gerreidae and Plotosidae . At station 6, 39 specimens of the species Plotosus anguillaris (family_ Plotosidae) , five Arius sp. (family Ariidae), and three Gerres sp. (family Gerreidae) were caught. At station 4, six specimens of Arius sp. and one P. anguillaris were ,obtained. These results are summarized in Table 2. Ariidae 16 .2% Naticidae 2.9% (Natica sp.) (Arius sp.) Buccinidae 1.5%csolenosteira sp.) Gerreidae N{]ssariidae 10.3% (Gerres sp .) (Pa ra onides sp.) Paraonidae 4.4% Iospilidae 1.5% ( Iospilus sp.) Plotosidae 58.8% (Plotosus anguillaris) Fig. 3. Percentage family abundance at Sungei Serangoon . Table 2. Abundance of the various families found in Sungei Serangoon.